This invention relates to distillation apparatus and distilling method. More particularly, the invention pertains to apparatus and method suited for distilling an easily polymerizable compound, such as a (meth)acrylic acid.
Distillation of a polymerizable compound, such as a (meth)acrylic acid, tends to produce a polymer which could cause clogging of a pipe. Conventionally, a polymerization inhibitor or molecular oxygen has been added to the compound to prevent such polymerization.
In a lower portion of a distillation tower, however, the temperature is generally high, so that the polymerization is likely to occur if the retention time of a liquid in the lower portion of the distillation tower is prolonged. When a polymer has been produced, operation of the distillation tower is stopped and the polymer is removed by chemical treatment or manual operation.
One potential approach to preventing the polymerization would be to shorten the retention time of the liquid. This approach, however, has a problem that vortex could occur in the liquid when its level in the distillation tower becomes low, making it difficult to carry out a distilling process in a stable fashion due to entrainment of gas caused by the vortex.
Another approach to the prevention of polymerization is introduced in xe2x80x9cDistillation Operationxe2x80x9d (McGraw-Hill) written by Kister. Kister indicates, in the drawing (FIG. 4.8(a)) on page 99 of the book, a method of maintaining the liquid level on the inside of a pot. This method, however, is likely to cause polymerization at a lower head of a distillation tower. Furthermore, the pot needs to have a large vertical length in this method, causing an increase in construction cost.
It is an object of the invention to provide a distillation apparatus and distilling method which are free from the problem residing in the prior art.
According to an aspect of the invention, a distillation apparatus comprises: a distillation tower; a bottom outflow portion for allowing a liquid from the bottom of the distillation tower to flow out of the distillation tower; and a pot portion provided between the bottom of the distillation tower and the bottom outflow portion, the pot portion having a cross-sectional area smaller than the cross-sectional area of the distillation tower, and larger than the cross-sectional area of the bottom outflow portion.
According to another aspect of the invention, an easily polymerizable compound is distilled by use of a distillation apparatus which comprises a distillation tower; a bottom outflow portion for allowing a liquid from the bottom of the distillation tower to flow out of the distillation tower; and a pot portion provided between the bottom of the distillation tower and the bottom outflow portion, the pot portion having a cross-sectional area smaller than the cross-sectional area of the distillation tower, and larger than the cross-sectional area of the bottom outflow portion.
The distillation apparatus and distilling method make it possible to effectively prevent polymerization in a distillation tower without causing entrainment of gas into a liquid and perform distilling operation in a stable fashion.
These and other objects, features and advantages of the invention will become more apparent upon reading the following detailed description in conjunction with the accompanying drawings.